502 



NA rURE 



[March 27, 1902 



At a meeting of the Edinburgh Mathematical Society on 

 March 14, the following resolutions in regard to the teaching 

 of elementary mathematics were agreed to: — (l) That the 

 primary object in teaching elementary mathematics is to afford 

 a mental training to the pupil. The commercial, technical or 

 professional applications of the subject are of secondary im- 

 portance in general education. (2) That there should be no 

 undue haste to begin the study of the calculus with a view to 

 its practical applications. (3) That pupils should not be en- 

 couraged in the unscientific practice of placing dependence on 

 rules or formula; which they do not understand. (4) That, in 

 teaching any branch of mathematics, concrete illustrations and 

 verifications including experimental, graphical and other 

 methods should, wherever jiracticable, accompany theory. (5) 

 That in e.\aminations particular methods of solution or demon- 

 stration should not, as a lule, be demanded, e-g., the use of 

 algebra should not be prohibited in answering questions in 

 arithmetic or geometry. (6) That there should not be in)posed 

 upon schools in any branch of mathematics a syllabus which 

 does more than indicate the order in which the main divisions 

 of a subject are to be taught. 



Dr. D. C. Oilman's reminiscences of the foundation and 

 early days of the Johns Hopkins University, given in the 

 current number of Scribiier s Magazine, contain several in- 

 teresting particulars concerning men connected with it. Johns 

 Hopkins left his fortune to be divided between a university and 

 a hospital, the two to be united in the promotion of medical 

 science. As the capital for the university was thus provided by 

 a single individual, there were no bodies to interfere with its 

 plans, and no public or treasury to conciliate. Given the idea 

 and the funds, all that had to be done was to produce the plan 

 of an institution which should aim at having national influence, 

 and should take to Baltimore, as teachers and students, the 

 ablest minds that could be attracted there. Rowland was an 

 assistant instructor in the Rensselaer Polytechnic Institute when 

 Dr. Oilman heard of him from General Michie, and the follow- 

 ing conversation occurred: — "What has he done?" I said. 

 " He has lately published an article in the Philosophical Maga- 

 zine,'" was his reply, " which shows great ability. If you want 

 a young man you had better talk with him." " Why did he 

 publish it in London," said I, "and not in the American 

 /ournal?" "Because it was turned down by the American 

 editors," he said, "and the writer at once forwarded it to Prof. 

 Clerk Maxwell, who sent it to the English periodical." When 

 Dr. Oilman had seen Rowland and reported upon his rare 

 powers to the trustees in Baltimore they said at once, " Engage 

 that young man and take him with you to Europe, where he 

 may follow the leaders in his science and be ready for a pro- 

 fessorship." This was done ; and the result is well known. 

 Huxley gave the inaugural address, but he had to deliver it 

 from memory, as he could not read the flimsies with which the 

 reporters to whom he had dictated the lecture on the previous 

 day had provided him. After this opening without music, 

 prayer or other benediction came the storm of indignation 

 from the religious papers. Referring to the opening, a Presby- 

 terian minister wrote to a friend : — " It was bad enough to 

 invite Huxley. It were better to have asked God to be present. 

 It would have been absurd to ask them both. I am sorry 

 Gilman began with Huxley. But it is possible yet to redeem 

 the University from the stain of such a beginning." It took 

 some years for the prejudice to wear away, but eventually the 

 idea of an undenominational university controlled by laymen 

 was accepted as reasonable, and Johns Hopkins' foundations 

 became renowned as places of freedom and progress. 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, January 30. — "The Distribution of 

 Magnetism as Affected by Induced Currents in an Iron 

 Cylinder when Rotated in a Magnetic Field." By Ernest 

 Wilson, Professor of Electrical Engineering, King's College, 

 London. Communicated by Sir W. H. Preece, F. K.S. 



One object of this research was to investigate the effect 

 which induced currents have upon the distribution of magnetism 

 in an iron cylinder when rotated about its longitudinal axis in a 

 magnetic field, the direction of which was normally at right 

 angles to the axis of rotation. The variables dealt with were 

 the total flux of magnetism between the poles of the magnet, 

 and the speed of rotation of the cylinder. By threading 



NO. 1 69 I, VOL. 65] 



insulated copper conductors through holes drilled in a plane 

 containing the longitudinal axis, E.M.F.'s due to the rate of 

 change of induction at different depths have been observed, 

 and therefrom the intensity of induction has been found. The 

 cylinder had a diameter of 25 4 cms., and its length was 

 25 '4 cms. It was rotated by aid of a worm and worm wheel. 

 I'eriodic times of 360, iSo, 90, 45 and 22 5 secimds have been 

 dealt with, and the normal induciion density B in the cylinder 

 has been varied from about 170 to 21,000 C.G.S. units per sq.cm. 



With small magnetic force, and a periodic time of 45 

 seconds, the value of B at the centre of the cylinder 

 is 'important as compared with its value at the surface, and 

 the phase-displacement between the two is relatively small. 

 With intermediate magnetic force, corresponding to high 

 average permeability in the iron, the value of B at the centre 

 became relatively small, accompanied by considerable phase-dis- 

 placement. In lact, with 22-5 seconds periodic time, B at the 

 centre was totally reversed in sign with regard to B at the 

 surface, or the lag was 180". With large magneiic force, B at 

 the centre again became important, and the phase-displacement 

 was again small. With a periodic time of 360 seconds, the 

 disturbances above described still existed, but they were small. 

 Similar efiects to the above were observed in the case of an iron 

 cylinder subjected to alternating magneiic force. 



The conclusion was that with an alternating magnetic force 

 applied axially to a cylinder of given diameter, the effects were 

 more severe than in the same cylinder (of length equal to 

 diameter) when rotated in a magnetic field as above described 

 at the same frequency, and for corresponding values in the 

 surface induction density. The results of these experiments 

 were applied to similar cylinders of different dimensions by an 

 application of the law of squares. The effects of induced 

 currents in the armature of a certain class of induction motor 

 were dealt with. It is shown that plates of iron 01 cm. thick 

 experience no serious deviation from uniform distribution when 

 rotated in a magnetic field, the direction of which was in the 

 plane of the plate, at frequencies lower than about 180. 

 Referring to Lord Kelvin's computation that the earth's 

 magnetism is travelling round the earth in the direction of the 

 sun with a periodic time relatively to the earth of 960 years, it 

 is pointed out that in a cylinder similar in all respects to the 

 one experimented upon,, but having a diameter equal to that of 

 the earth, a periodic time of 960 years would produce similar 

 magnetic and electric events as would be observed in the above 

 cylinder if it could be rotated with a periodic time nearly two 

 million times as fast as the fastest speed in these experiments. 

 On the other hand, with a cyljndei; oooooooi cm. diameter, 

 7 X 10'^ revolutions per second wculd be required to produce the 

 disturbances observed in these experiments. 



March 6. — "The Differential Equations of Fresnel's Polari- 

 sation-vector, with. an Extension to the Case of .Active Media." 

 By James Walker, M.A. Communicated by Prof. Clifton, F.R.S, 



In many problems of optics we require the differential equa- 

 tions that the polarisation-vector has to satisfy, and the surface 

 conditions that subsist at the interface of different media. These 

 may be deduced from the principle of interference combined 

 with the experimental laws of the propagation of light, without 

 making any assumption respecting the character of (he ether 

 and the nature of the luminous vibrations. In crystalline media, 

 Fresnel's theorem of the ellipsoid of polarisation affords the 

 required relations between the wave-velocity and the directions 

 of the wave-normal and of the polarisation-vector ; in the case 

 of active media, extensions of this theorem lead to similar equa- 

 tions giving the wave-velocity in terms of the direction-cosines 

 of the wave-normal and the complex direction-cosines of the 

 vector of a stream of elliptically polarised light. The differential 

 equations are then deduced by applying the principle of inter- 

 ference. The surface conditions are obtained by assuming that 

 the transition between two media takes place by a rapid con- 

 tinuous change of their properties and that the differential 

 equations hold witljjn the region of variation. 



Royal Astronomical Society, March 14. — Dr. J. W. L. 

 Olaisher, president, in the chair. — The secretary read a paper 

 by Dr. Slitchell, of Xew York, on the flash spectrum at the 

 Sumatra eclipse of May, 1901. Mr. Fowler gave reasons for 

 doubting the correctness of Dr. Mitchell's view that the flash 

 spectrum represents the upper portion of the layer of gas which, 

 by absorption, gives the Fraunhofer lines. — .\ paper by Prof. 

 Barnard on Nova Cygni, 1S76, was, partly read. — Mr. Maw 

 presented a series of double star measures made by him in the 



